Bump @bower_components/backbone from 1.3.3 to 1.4.0 in /build

Bumps [@bower_components/backbone](https://github.com/jashkenas/backbone) from 1.3.3 to 1.4.0.
- [Release notes](https://github.com/jashkenas/backbone/releases)
- [Commits](jashkenas/backbone@8ec8860...5de45fc)

Signed-off-by: dependabot[bot] <support@dependabot.com>

build/package.json

@@ -10,7 +10,7 @@
   "homepage": "https://github.com/owncloud/",
   "contributors": [],
   "dependencies": {
-    "@bower_components/backbone": "jashkenas/backbone#1.3.3",
+    "@bower_components/backbone": "jashkenas/backbone#1.4.0",
     "@bower_components/base64": "davidchambers/Base64.js#1.0.2",
     "@bower_components/blueimp-md5": "blueimp/JavaScript-MD5#1.0.1",
     "@bower_components/bootstrap": "twbs/bootstrap#3.3.6",

build/yarn.lock

@@ -2,10 +2,10 @@
 # yarn lockfile v1
 
 
-"@bower_components/backbone@jashkenas/backbone#1.3.3":
-  version "1.3.3"
-  uid "8ec88604732944f197b352a6be22c8216ea9d3a1"
-  resolved "https://codeload.github.com/jashkenas/backbone/tar.gz/8ec88604732944f197b352a6be22c8216ea9d3a1"
+"@bower_components/backbone@jashkenas/backbone#1.4.0":
+  version "1.4.0"
+  uid "5de45fc9e1cbe5f61cf459067207bbe73451ac91"
+  resolved "https://codeload.github.com/jashkenas/backbone/tar.gz/5de45fc9e1cbe5f61cf459067207bbe73451ac91"
   dependencies:
     underscore ">=1.8.3"